\begin{tikzpicture}[>=Stealth]
    \foreach \baseline / \name / \formula in
        {6/{正弦}/{$\displaystyle \frac y r$}, 
         4/{余弦}/{$\displaystyle \frac x r$},
         2/{正切}/{$\displaystyle \frac y x$},
         0/{余切}/{$\displaystyle \frac x y$}}
    {
        \draw (0, \baseline) circle [x radius=0.6cm, y radius=0.8cm];
        \node at (0, \baseline + 0.3) {$\alpha$};
        \node at (0, \baseline - 0.3) {$\vdots$};

        \draw (3, \baseline) circle [x radius=0.6cm, y radius=0.8cm];
        \node at (3, \baseline + 0.3) {\formula};
        \node at (3, \baseline - 0.3) {\vdots};

        \node at (1.5, \baseline + 0.5) {\name};
        \draw [->] (1.0, \baseline + 0.1) -- (2.0, \baseline + 0.1);
    }
\end{tikzpicture}
